1. Field of the Invention
This invention relates to sealing articles for cavities, and methods for making and using them. More particularly, this invention relates to sealing articles for channels in automobiles or other land vehicles, boats or other marine vehicles, aircraft or other aerospace vehicles, structures, including land and marine structures, and the like, wherever it is desirable to seal a cavity against the passage of air, moisture, fluids, particulates, and the like. In a particular aspect, this invention relates to the sealing of channels, such as pillars, in the body structure of automobiles and similar vehicles; and the invention will be discussed primarily with respect to that aspect.
2. Description of Related Art
During the fabrication of automobiles, trucks, and similar vehicles, many body components present cavities that require sealing to prevent the ingress of moisture and contaminants that can cause corrosion of the body parts. This is especially true with respect to unibody structures, where a heavy frame is replaced by a structurally designed space frame that inherently presents a number of moisture- and contaminant-collecting cavities. These cavities also serve as passages through which road and engine noise and other sounds may be transmitted during normal use of the vehicle. For example, the upright post structure of a vehicle body defining a portion of a window opening presents an elongated cavity that can collect moisture and contaminants and also transmit sounds unless the cavity is at least partially filled with a sealant material that blocks the passage of moisture and debris and that also serves as a baffle for muting sounds that would otherwise be transmitted along the length of the cavity and then radiate into the passenger compartment of the vehicle. There are other irregular cavities in a vehicle body that desirably are sealed to prevent moisture and contaminants from entering that area and being conveyed to other parts of the vehicle body.
Many attempts have been made to seal these cavities; and some techniques and products for this purpose are described in U.S. Pat. Nos. 5,266,133 and 5,373,027 (Hanley et al.), 5,212,208 and 5,160,465 (Soderberg), 5,040,803 (Cieslik et al.), 4,989,913 (Moore, III), and 4,874,650 (Kitoh et al.), among others. The disclosures of these and other documents referred to in this application are incorporated herein by reference.
A currently favored technique in automobile cavity sealing is the use of a heat-activated sealing foam material. Typically, a mass of a material capable of expansion (foaming) at elevated temperatures, i.e. a thermoplastic mixture containing both a heat-activated foaming agent and a heat-activated crosslinking agent, is placed on a tray or other mechanical support, usually made from sheet metal or a molded high temperature thermoplastic, that is capable of being mechanically fastened within the cavity. Because automobile bodies are now typically coated by total immersion in phosphating, rustproofing, electrocoating, and other paint baths to ensure that the interiors of all open cavities are coated, the sealing article (the tray, together with the mass of foamable material), should not fill the cavity cross-section before foaming, so that the coatings may enter the cavity during immersion and drain from it after removal from the bath. As the automobile body is passed through an oven to cure the coating to the metal of the body, the foamable mass expands to fill the cavity cross-section and seal to the walls of the cavity. While this technique has proved generally satisfactory, it suffers from two principal disadvantages. First, because the foam material is not self-supporting during foaming, it is subject to sagging before the foam crosslinks, and therefore requires support. This problem is particularly severe when the axis of the cavity to be sealed is approximately horizontal, so that the foam material (which is perpendicular to the cavity axis) is approximately vertical, and the sagging therefore tends to limit expansion of the foam toward the upper parts of the cavity walls. The tray required to support the foam during expansion and sealing adds to both the weight and cost of the seal. Second, because the foamable material is supported during expansion, interfacial adhesion of the molten foaming material to the support restricts lateral expansion of the foam, so that greater expansion occurs perpendicular to the support (along the longitudinal axis of the cavity rather than towards the cavity walls). As a result, sealing may be incomplete, and a greater amount of foamable material is used in an attempt to ensure adequate sealing, also adding to both the weight and cost of the seal. This problem is particularly severe when the cavity to be sealed is highly irregular in cross-section or has a sharply acute angle, when a considerable excess of foamable material may be used to attempt to ensure that the foam fills the cavity cross-section and penetrates to the vertex of the angle.
In certain uses, particularly in the sealing of the vertical pillars of automobile bodies, it may be desirable to be able to provide a drain passage within the pillar. For example, in automobiles with sunroofs, it is necessary to provide a drain passage for water which might otherwise accumulate in spaces around the sunroof. Usually, this drain passage is created by a drain tube from the sunroof area passing down one or both of the "A" pillars (the pillars on either side of the front window of the automobile). Thus a passage must be provided through any seal in that pillar. Three different solutions are currently used for this problem. One is to allow the pillar itself to serve as the drain passage and to provide a drainage plug through the cavity seal. The drainage plug has a tortuous path through which fluids may drain, but which is intended to reduce sound travel through the plug. This simple solution has the two disadvantages of allowing draining fluid to contact the inside of the pillar as it drains and of allowing sound infiltration, especially the infiltration of high frequency sound, through the drain plug since the tortuous path is still open. A second solution is to use a conventional seal with a hole, and a drain hose passing through the hole. Here the disadvantages of the drain plug are avoided, but the need for the hose to be emplaced before the vehicle frame is fully assembled means that a hose capable of withstanding the high temperatures encountered in the paint bake ovens must be used, increasing the cost. A third solution is to leave the pillars open through the painting process, then install a low cost hose through the pillar and seal it in place by injection of a foaming material, such as a two-part urethane, into the pillar. This solution also provides an effective seal, but at the increased cost of capital equipment for preparation and injection of the urethane foam, ventilation, etc., and with the need for an additional step in the vehicle assembly process.
It would be desirable to produce a cavity sealing article, especially a sealing article for use in a channel in a land, marine, or aerospace vehicle, such as a pillar in the body structure of an automobile or similar vehicle, that could be prepared readily and inexpensively, would be readily handleable and emplaceable within a cavity to be sealed without requiring special tooling, would be readily activatable by elevating the cavity temperature to such temperatures as are commonly encountered in operations on the vehicle body (e.g. 115.degree. C. to 250.degree. C. for automobile paint ovens), and, on activation, would provide an effective seal against infiltration of air, moisture, other undesirable fluids and particulates, and sound. Desirably, such a sealing article would also permit the passage of drain hoses and the like through the seal.